No extra apk needed for me
I have tested with a headphone from my LG gw620 and works fine (I am on stock unrooted jellybean Moto G).
I can answer calls by pressing button on earphone's mic. During a call if I press it silences my mic and if i press it reactivates mic. (I can't end call, so)
In stand by mode a short press triggers my last multimedia apk used (radio, music, etc..) and while playing them if i press button I get pause.
Long press always ends in same end: google Voice search.
::Motorola Milestone 2:: Test phone KitKat 4.4.2
::Motorola Moto G:: KitKat 4.4.2 All Stock